A conventional magnetic tunnel junction includes a pinned ferromagnetic layer, a sense ferromagnetic layer and an insulating tunnel barrier sandwiched between the ferromagnetic layers. Relative orientation and magnitude of spin polarization of the ferromagnetic layers determine the resistance of the magnetic tunnel junction. Generally, the resistance of the magnetic tunnel junction is a first value (RN) if the magnetization of the sense layer points in the same direction as the pinned layer magnetization (referred to as a “parallel” magnetization orientation). The resistance is increased to a second value (RN+ΔRN) if the magnetization orientations of the sense and pinned layers point in opposite directions (referred to as an “anti-parallel” magnetization orientation). The magnetic tunnel junction has an intermediate resistance (RN<R<RN+ΔRN) as the sense layer magnetization is rotated from one direction to the other.
Magnetic tunnel junctions can be used as magnetic sensors in read heads. The magnetic tunnel junction of a read head can detect data stored on a magnetic storage medium such as a hard disk drive.
Magnetic tunnel junctions can be used as memory elements in magnetic random access memory (MRAM) devices. The two magnetization orientations, parallel and anti-parallel, represent logic values of “0” and “1.” A logic value may be written to a magnetic tunnel junction by setting the magnetization orientation to either parallel or anti-parallel. The orientation may be changed from parallel to anti-parallel or vice-versa by applying the proper magnetic field to the magnetic tunnel junction. The logic value may be read by sensing the resistance of the magnetic tunnel junction.
FM coupling between the pinned and sense layers can cause problems with magnetic tunnel junctions. In read heads, the FM coupling can cause readback signal distortion. Bias techniques can be used to correct the signal distortion. However, the bias techniques tend to be complex to implement and costly to fabricate.
In magnetic memory elements, the FM coupling can render magnetic tunnel junctions unusable. Unusable magnetic tunnel junctions can reduce MRAM performance, increase fabrication cost, and increase the complexity of read circuits.